The need for the use of modern technologies for diagnosing the work of the developed facilities and clarifying information on the productivity of the target formation arises when making decisions on the control of development, including designing and planning various kinds of technological measures, as well as conducting research to monitor the current state of existing wells. Traditional methods for monitoring the inflow profile are not always effective and cost-effective, especially when it comes to hard-to-recover reserves. One of the most progressive solutions is the use of marker studies based on the selection of markers from the produced fluid and their subsequent identification in samples taken at the wellhead . The main advantage of this technology is that there is no need to suspend work for hoisting operations in order to obtain informative field-geophysical data during well operation. Moreover, the undoubted advantage of marker monitoring is its long-term nature since the technology allows continuous downhole data obtaining within several years. The subject of this work is a gas well with an extended horizontal wellbore, in which the 18-stage hydraulic fracturing using marked quartz polymer-coated sand was carried out.